Oil and gas drilling rigs are located throughout the world, both on land and at sea. There are important differences between the types of drilling rigs used for inland sites compared to those used for offshore drilling. An offshore drilling rig is typically very large, and may be made as a unitary structure. The electrical power generation and distribution system can be built on an offshore rig before the rig is moved into its operating location. This allows for hardwired connections and other permanent or semi-permanent electrical connections in the electrical distribution system.
Many inland oil and gas drilling rigs are much smaller than their offshore counterparts. It is common for inland rigs to be constructed in a more modular form, with the various parts of the rig being put together at the drilling location. A rig of this type may be hauled to the drilling site on one or more trucks. Because the rig is delivered in parts and assembled on site, the electrical distribution system is often prepared on site, as well. It is not common to have an electrical power distribution system pre-wired for a smaller inland drilling rig.
The field assembly and installation of many inland drilling rigs has led to widespread use of single pole electrical connectors that can be prepared in the field. These connectors take different forms, including pin and collet style connectors or plug and receptacle style connectors. The latter require very tight fits between the plug and the receptacle to ensure minimal resistance to the high current loads and to prevent the connections from pulling apart during use. Different types of locking mechanisms are also typically used with plug and receptacle connectors to ensure the connections do not inadvertently pull apart. There remains, however, a need to ensure a very tight fit between the plug and receptacle.
To achieve the needed fit, a split-pin design has been used in oilfield applications for many years. In this design, the male pin connector, which could be part of either the plug or receptacle, has a conductive pin that is cut into two halves by a slot cut along the length of the pin. This slot allows the two halves of the pin to be pushed together, thus reducing the diameter of the pin, or pried apart, thus increasing the diameter of the pin. The pin's diameter is variable, and can be adjusted to provide a needed tight fit between the male and female components of a plug and receptacle type connection.
The basic variable diameter pin design is disclosed in a number of patents, including, for example, U.S. Pat. Nos. 3,644,869 and 3,662,296. The disclosures of these two patents are hereby incorporated by reference. Each of these references disclose a conductive pin having a slot cut along its length. The '869 reference discloses use of a Belleville washer positioned within the slot.
The Belleville washer or spring is well-known in the art as a means of providing a pre-selected stress within a small slot or groove. In the '869 reference, the Belleville washer positioned within the slot allows for small adjustments to the diameter of the conductive pin. The disclosed configuration includes a fixing stud, which is driven into the pin and exerts a force against the Belleville washer. By increasing this force, the two sides of the pin may be separated slightly, resulting in a slight increase in the diameter of the pin. The male pin and female receiver of this type of connection are machined for a very tight fit, so only small adjustments to the diameter of the pin should be needed to ensure the necessary fit is obtained.
This basic type of variable-diameter pin design has been in use in oilfield applications for many years. The tip end of the pin is often covered by a protective, insulating safety cap, which helps protect workers from inadvertently contacting a live connector. The insulating safety cap is typically just more than one-half inch long, and covers about 20-25% of the length of the conductive pin. A safety cap of this type is widely used, and is discussed in the '296 reference identified above and incorporated into this application.
The Belleville washer adjustment mechanism in the prior art male connector is positioned about one inch from the tip end of the pin. A port is typically drilled or cut into one side of the pin about one inch for the tip of the pin. This port is typically threaded. The Belleville washer or washers are positioned with their center aligned with the threaded port. An adjustment screw is screwed into the threaded port until it exerts pressure on the Belleville washer.
The pin is then checked for fit with a female receiver. If the male pin fits too loosely, the adjustment screw is tightened, which exerts more force on the Belleville washer, and thus causes the two halves of the split pin to separate slightly. The fit is then checked again. This process is repeated until the desired fit is achieved.
These adjustments and tests are done prior to use of the connectors in the field. This design does allow for field-adjustment of the variable-diameter pin, but that option is often undesirable. The fit tolerances of these components are so tight that even small temperature differences between male and female will result in an improper fit. Field operators often lack the experience or expertise needed to make the fine adjustments required for these types of connections. Though a field-adjustable pin may seem advantageous at first blush, it is, in fact, a undesirable condition. Field adjustment of these components is likely to cause much more harm than good.
In the prior art design, the adjustment port is typically beveled. The allows for easy placement of the adjustment screw in the port, and facilitates the placement of a screwdriver, Allen wrench, or other tightening means into the port for adjustment.
Through the many years of use of this type of variable-diameter pin connector, a number of problems have arisen. First, the pin is field-adjustable, as explained above. This is not desirable in practice. Second, the beveled opening of the port tends to become clogged with dirt and debris in the field. The materials clogging the port may prevent the male pin and female receiver from obtaining the needed tight fit. If gritty materials clog the port, those materials may come out during assembly of the connection and score both the male pin and the female receiver.
A third problem arises from burrs left by the cutting of the bevel. If a burr is left, it is likely to cause damaging scoring of the female receiver when the connection is made up in the field. A forth problem arises from the drilling of the port, the tightening of the adjustment screw or both. This problem is the creation of a very small dimple on the outside of the pin as a point opposite the location of the adjustment port. The dimple is small, but given the very tight fit required for these connectors, even a small irregularity can result in a poor fit between the male pin and female receiver.
In this traditional design, the last one-half inch or so of the pin is of slightly less outer diameter to allow for placement of the insulating safety cap. When the cap is in place, the outer diameter of the cap is the same as, or, more typically, slightly less than that of the main body of the pin. A slightly reduced diameter safety cap allows for easier insertion of the male pin into the female receiver.
An improved variable-diameter pin design is needed. Though the traditional design has proved adequate, the problems identified above show that there is clearly room for improvement. These types of connectors are used in applications where current levels of hundreds of amps, and even more than one-thousand amps, are quite common. With such high amp loads, even a very small increase in the resistance of a connector can result is substantial resistive heating, which can damage insulation and other materials, thus leading to a domino effect of failures. Given the context in which these connectors are used, it is important to maintain the best possible electrical connection with the lowest possible resistance. The problems identified above tend to produce slight increases in the resistance of the connection.
The present invention addresses the problems described above. An improved, variable-diameter pin design is disclosed. The adjustment mechanism is positioned near the tip of the pin and under the safety cap. This design prevents field adjustment of the pin because the safety cap is not a field-removable item. It eliminates clogging of the adjustment screw port. It prevents burrs from scoring the female receiver because the port is covered by the safety cap, and because the port is cut into the slightly reduced diameter tip portion of the pin. Finally, any dimple created opposite the adjustment screw port is also covered by the safety cap and is located in the smaller diameter tip portion of the pin. For this reason, a small dimple created opposite the port will have no adverse effect on the performance of the connector.
These and other objects and advantages of the present invention shall become apparent from the following descriptions of the invention. In one preferred embodiment, the present invention has an electrically conductive pin having a contact region, a tip, and a slot extending along most of the contact region and to the tip, wherein the slot extends entirely through the pin whereby the pin is divided into two semi-cylindrical members; an insulating safety cap positioned over the tip of the conductive pin; and, an adjustment mechanism positioned under the insulating safety cap and configured to vary the width of the slot and thus the effective diameter of the conductive pin.
In another preferred embodiment, the present invention includes the steps of making a cylindrical, electrically conductive pin having a contact region and a tip, wherein the outside diameter of the tip is less than the outside diameter of the contact region; cutting a slot in the conductive pin extending from the tip and through most of the contact region of the pin such that the pin is divided into two semi-cylindrical members; installing an adjustment mechanism within the slot of the conductive pin and in the tip of the conductive pin; determining whether the contact region of the conductive pin has a desired outside diameter; if the contact region of the conductive pin does not have the desired outside diameter, varying the effective diameter of the conductive pin by adjusting the adjustment mechanism; repeating the prior two steps until the contact region of the conductive pin has the desired outside diameter; and, installing an insulating safety cap over the tip of the conductive pin such that the adjustment mechanism is rendered inaccessible during normal use. These and other embodiments are described in more detail below.